I need help with reverse polarity protection scheme

Thread Starter

AIBang

Joined Feb 3, 2024
26
I could not clearly understand in which situations the MOSFETs would turn on and off and how the signals would reach the labels. Can you read this diagram to me?


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LowQCab

Joined Nov 6, 2012
4,053
That's a good question.

Why would anyone want to slog though an
unknown, cryptic Schematic when You don't even give a
description as to what You are attempting to do ?

Where did the Schematic come from, and why do You want to use it ?
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Thread Starter

AIBang

Joined Feb 3, 2024
26
You're right, I'm new. This diagram is the reverse polarity protection diagram of the TIDA-010216 board. Its purpose is to create a signal on the labels according to the connection status of the charger and to understand whether there is a reverse connection. Most_Cell label is the voltage supplied from the battery. Pack-label is the negative pole of the Charger.
 

MisterBill2

Joined Jan 23, 2018
18,442
I find it very difficult to read the text on the drawing. I also find that the scheme for revers polarity protection is not obvious.
So I have questions: What DC voltage is the protection intended to be used with, and what is the anticipated load current maximum? And what voltages can the unknown load use to function as intended.
 

Thread Starter

AIBang

Joined Feb 3, 2024
26
I find it very difficult to read the text on the drawing. I also find that the scheme for revers polarity protection is not obvious.
So I have questions: What DC voltage is the protection intended to be used with, and what is the anticipated load current maximum? And what voltages can the unknown load use to function as intended.
You can access the information you are looking for more accurately from the link. I hesitate to give misleading information because I do not have full information. You can understand it better if you read the design guide in the link yourself.
https://www.ti.com/tool/TIDA-010216
But if I were to answer, the load current should be a maximum of 3A. The load voltage range may be greater than or equal to 48V. We can consider the Most_Cell voltage and the load voltage as equal.
 

MisterBill2

Joined Jan 23, 2018
18,442
OK, that information is close enough. Really, a simple series diode can provide protection, and a relay operated by a diode can provide a lot of current. YES, it is using an electro-mechanical device ans so it is not nearly as "sexy" as a complex circuit, but once correctly assembled it will probably outlast whatever it is protecting.
 

LowQCab

Joined Nov 6, 2012
4,053
There is almost a ~100% chance that the Circuit will perform exactly as it claims,
that is, as long as You carefully follow the recommendations in the Instructions.

Why do You need to know how it works ?

Do You intend to create your own modified version of this Circuit ?
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Thread Starter

AIBang

Joined Feb 3, 2024
26
There is almost a ~100% chance that the Circuit will perform exactly as it claims,
that is, as long as You carefully follow the recommendations in the Instructions.

Why do You need to know how it works ?

Do You intend to create your own modified version of this Circuit ?
.
.
.
Yes, when I create my own version, I want to understand exactly how the circuit works so that I can understand whether it works correctly when testing the pcb.

For example, when I simulate the circuit, I cannot see a signal from the CHG_WAKE label when the charger is connected correctly. That's why I think there is something I don't understand or missed.
 

BobTPH

Joined Jun 5, 2013
8,932
If I were so worried about reverse polarity, I would just use a bridge rectifier on the power input. That way it works with either polarity or even AC input.
 

crutschow

Joined Mar 14, 2008
34,392
Another simple way to protect against reverse polarity for a positive supply, with minimum voltage drop, is to use a P-MOSFET with its source drain to the supply, the gate to ground, and the drain source to the device being protected.
It's forward drop is just the device current times the MOSFET on-resistance.

Edit: The connection should be MOSFET drain to the plus supply and its source to the powered device.
 
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MisterBill2

Joined Jan 23, 2018
18,442
It might be difficult to get a mosfet without that pesky internal reverse diode, which could tend to conduct if the polarity was reversed.
 

crutschow

Joined Mar 14, 2008
34,392
It might be difficult to get a mosfet without that pesky internal reverse diode, which could tend to conduct if the polarity was reversed.
(Head slap) Sorry, I mixed up the source and drain connections.
The drain goes to the plus supply and the source to the powered device.
Then that "pesky" diode is only forward biased with a plus supply polarity until the MOSFET turns ON at its gate-source threshold voltage.
It's reverse biased if a negative supply is applied (sim below):
This works because a MOSFET conducts equally well in either direction when biased ON.

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